The present invention relates generally to the manufacture of injection molded articles and, more particularly, to a single-piece injection molded rack and the mold for producing the same. In a preferred form, the invention is advantageously employed to provide a plastic test tube rack for medical and laboratory use.
Test tube racks are widely used where it is desirable to perform biological or chemical tests in a related sequence or on a related group of specimens. Before performing such tests it is frequently necessary to simultaneously sterilize the test tubes and rack. Many operations, as well, require that the rack, test tubes, and their contents be placed in an incubator to facilitate the chemical reaction or growth of organisms within the media under test. Often, the autoclaves or incubators available to a particular laboratory have limited internal space, making it highly desirable to have a rack that will hold a dense array of test tubes.
As test tubes are more tightly grouped, however, it becomes necessary that the individual tubes be maintained in proper alignment so that material may be introduced or withdrawn from the tubes in an orderly, sequential manner. As well, the contents of the tube must remain readily observable by the technician.
The conventional wire rack is extensively employed in an effort to achieve these goals. Typically, such racks are three-tiered structures, the individual tiers being rectangular grids formed by welding together individual metal rods. The tiers are then operatively joined by welding additional metal rods to each tier, vertically from top to bottom. The completed assembly is thereafter coated with a thin layer of conforming plastic to protect the metal against corrosion and chemical attack. However, with usage, the plastic coating wears off, leading to rust and corrosion which render the racks unusable.
While such wire racks function satisfactorily, they are costly to produce and, because of their weight, costly to ship in quantity. These costs are shared by the end user, making wire racks economically unsuitable for use as a disposable item of laboratory equipment. These racks, thus, are ill suited for analytical operations in which the hazardous substances used dictate disposal of both test tubes and racks.
For such hazardous procedures, test tubes made of plastic are commercially attractive. Although a number of plastic test tube racks has been heretofore proposed, none has achieved the dense packing and tube visibility advantages of the wire rack. The usual approach of such plastic racks has been to provide multiple plastic plates, each of the plates having a plurality of apertures for receiving the test tubes. Typically, the apertures are circular to conform to the shape of the test tubes. Often the plates are separately molded and thereafter assembled using other separately molded components. Since these single plates are relatively thin, they are easily formed by a simple mold section having projecting circular cores that cooperatively mate against a planar mold half. The general design and construction of steel injection molds, however, does not allow for compact and dense placement of metal cores to mold holes for various reasons. For example, the steel sections between the cores that mold the holes become too thin and flimsy for practical application. Also, the effective placement of cooling channels becomes impractical. Consequently, these multilevel plastic test tube racks have generally widely spaced apertures and are assembled from several separately molded components.
In addition to the limitation on aperture density, this type of plastic test tube rack requires assembly, thus yielding up some of the cost benefits associated with plastic manufacture. It would be most desirable if a plastic test tube rack could be manufactured as a single piece in a fully automated mold. It would be particularly advantageous if such a rack could also provide the dense two-dimensional test tube arrays and high visibility afforded by wire racks.
The present invention achieves the objectives of equalling the test tube density and viewability advantages of the wire rack. In accomplishing these objectives in a single-piece, one-shot injection molding operation, the present invention significantly reduces the manufacturing cost associated with assembling a wire rack from individual metal rods as described above. As a consequence, the present invention provides a rack that can be offered more economically to the end user. Since the unique configurations of both the rack and the mold are adapted to a wide variety of plastic materials, racks can be produced to exhibit functional characteristics ranging from durability and reusability to single-use disposability.